Bulletin of the American Physical Society
68th Annual Meeting of the APS Division of Fluid Dynamics
Volume 60, Number 21
Sunday–Tuesday, November 22–24, 2015; Boston, Massachusetts
Session L25: Biofluids: Cell Interactions and Transport |
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Chair: Jeremie Palacci, UCSD Room: 304 |
Monday, November 23, 2015 4:05PM - 4:18PM |
L25.00001: Emergent properties in experiments with synthetic micro-swimmers Jeremie Palacci Self-propelled micro-particles are intrinsically out-of-equilibrium. This renders their physics far richer than passive colloids and give rise to the emergence of complex phenomena e.g. collective behavior, swarming... I will present a variety of non-equilibrium phenomena observed with experimental realization of synthetic micro swimmers: self-assembly, sensing of the environment, or effective interactions, in the absence of any potential. [Preview Abstract] |
Monday, November 23, 2015 4:18PM - 4:31PM |
L25.00002: Chaotic mixing by microswimmers moving on quasiperiodic orbits Mir Abbas Jalali, Atefeh Khoshnood, Mohammad-Reza Alam Life on the Earth is strongly dependent upon mixing across a vast range of scales. For example, mixing distributes nutrients for microorganisms in aquatic environments, and balances the spatial energy distribution in the oceans and the atmosphere. From industrial point of view, mixing is essential in many microfluidic processes and lab-on-a-chip operations, polymer engineering, pharmaceutics, food engineering, petroleum engineering, and biotechnology. Efficient mixing, typically characterized by chaotic advection, is hard to achieve in low Reynolds number conditions because of the linear nature of the Stokes equation that governs the motion. We report the first demonstration of chaotic mixing induced by a microswimmer that strokes on quasiperiodic orbits with multi-loop turning paths. Our findings can be utilized to understand the interactions of microorganisms with their environments, and to design autonomous robotic mixers that can sweep and mix an entire volume of complex-geometry containers. [Preview Abstract] |
Monday, November 23, 2015 4:31PM - 4:44PM |
L25.00003: Preferential Transport Theory for Beta-Amyloid Clearance from the Brain Mikhail Coloma, David Schaffer, Paul Chiarot, Peter Huang The failure to clear beta-amyloid from the aging brain leads to its accumulation within the walls of arteries and to Alzheimer's disease. However, the transport mechanism for beta-amyloid clearance is not well understood. In this study, we propose a preferential transport theory for flow within the vascular walls in the cerebral arterial basement membrane. The flow conduit within the arterial basement membrane is modeled as an annulus between deformable concentric cylinders filled with an incompressible, single-phase Newtonian fluid. The transport is driven by arterial lumen deformation induced by heart pulsations superimposed with reflected boundary waves. Our theory predicts that while the overall arterial wave propagation is in the same direction as the blood flow toward the capillaries, a reverse flow in the basement membrane can be preferentially induced toward larger arteries. This has been suggested as a potential clearance pathway for beta-amyloid. We estimate the magnitude of the reverse transport through a control volume analysis which is corroborated by numerical solutions of the Navier-Stokes equations. Bench-top experiments to validate our computational models are presented. [Preview Abstract] |
Monday, November 23, 2015 4:44PM - 4:57PM |
L25.00004: Probing the Biophysics behind Flow-induced Amyloid Crystallization Samantha McBride, Sean Sanford, Juan Lopez, Amir Hirsa Agitation of fluid is known to induce formation of amyloidogenic species from native protein, yet the exact biophysical mechanism is unknown. Previous investigations indicate that shearing flows are important to formation, suggesting that amyloid crystallization is not a simple transport-limited reaction. Shear-induced deformation of protein monomers has been proposed, yet extensional forces used in most experiments are insufficient to pull apart the hydrogen bonds that constrain protein monomers in a folded state. Other hypotheses suggest that flow induces fibrillization via alignment of protein monomers or by enhancing transport to hydrophobic interfaces. Experiments using a uniform Couette device with a rotating outer wall have shown that even minute Reynolds numbers result in enhanced crystallization kinetics. Furthermore, experiments using two highly similar proteins with different protein-protein binding affinities have provided clues towards isolation of the biophysical mechanism. Experimental evidence from the current work will be presented alongside evidence from the literature, and the relative merits of different hypotheses regarding the mechanism of shear-induced crystallization will be discussed. [Preview Abstract] |
Monday, November 23, 2015 4:57PM - 5:10PM |
L25.00005: Optimizing an undulating magnetic microswimmer for cargo towing Yizhar Or, Emiliya Gutman One of the promising applications of robotic microswimmers is towing a cargo for controlled drug delivery, micro-surgery or tumor detection. This capability has been demonstrated by the magnetically-actuated microswimmer of Dreyfus et al [Nature 2005] in which a red blood cell was attached to a chain of magnetic beads connected by flexible DNA links. A key question is what should be the optimal size of the magnetic tail for towing a given cargo. This question is addressed here for the simplest theoretical model of a magnetic microswimmer under planar undulations - a spherical load connected by a torsion spring to a magnetized rigid slender link. The swimmer's dynamics is formulated assuming negligible hydrodynamic interaction and leading-order expressions for the resulting motion are obtained explicitly under small amplitude approximation. Optimal combinations of magnetic actuation frequency, torsion stiffness, and tail length for maximizing displacement or average speed are obtained. The theoretical results are compared with several reported magnetic microswimmers, and also agree qualitatively with recent results on cargo towing by screw rotation of magnetic helical tails [Walker et al, ACS Nano Letters 2015]. [Preview Abstract] |
Monday, November 23, 2015 5:10PM - 5:23PM |
L25.00006: Self-assembled controllable microswimmers Galien Grosjean, Guillaume Lagubeau, Alexis Darras, Geoffroy Lumay, Maxime Hubert, Nicolas Vandewalle Because they cause a deformation of the interface, floating particles interact. In particular, identical particles attract each other. To counter this attraction, particles possessing a large magnetic moment $\vec{m}$ are used. When $\vec{m}$ is perpendicular to the surface, dipole-dipole interaction is repulsive. This competition of forces can lead to the spontaneous formation of organized structures. By using submillimetric steel spheres for which $\vec{m} \propto \vec{B}$, interdistances in the system can be precisely tuned. Here, we deform these self-assemblies by adding a horizontal contribution $\vec{m}_x$ to the magnetic moment. Time reversal symmetry is broken in the system, leading to locomotion at low Reynolds number. Moreover, swimming direction depends on the orientation of field, meaning that swimming trajectories can be finely controlled. A model allows to understand the breaking of symmetry, while a study of the vibration modes gives further informations on the dynamics of this sytem. Because this system forms by self-assembly, it allows miniaturization with applications such as cargo transport or solvent flows. It is highly versatile, being composed of simple passive particles and controlled by magnetic fields. [Preview Abstract] |
Monday, November 23, 2015 5:23PM - 5:36PM |
L25.00007: Viscous constraints on squirmer microswimmers approaching suspended particles Mehdi Jabbarzadeh, Henry C. Fu Microscopic self-propelled organisms often approach other particles to capture food, mate, or find new environments. The viscous Stokes flow around these small organisms push away particles, severely hindering approach. Previously, we investigated approach hydrodynamics by modeling a swimming organism as a sphere pushed by a constant force towards a force-free spherical target particle. We measured approach efficiency by examining how far the swimmer must travel before getting close to the target. For targets which are of bigger or comparable size to the swimmer, the swimmer travels less than 1.5 times the initial separation distance; for smaller targets the swimmer must travel farther, making approach infeasible. The constant force reliably models propulsion by a flagellum, but many microorganisms feed by using cilia-coated surfaces for propulsion or generation of feeding currents. Therefore, here we consider a force-free spherical squirmer model for the swimmer approaching a spherical force-free target particle. For squirmers, the ``squirmer parameter'' distinguishes whether the swimmer is a puller or pusher. We find that pullers can always approach any size target and a larger squirmer parameter will generate a stronger feeding current leading to less traveled distance. On the other hand, pushers approach targets only when the squirmer parameter is less than 1; for values larger than 1, the swimmer cannot get close to the target. [Preview Abstract] |
Monday, November 23, 2015 5:36PM - 5:49PM |
L25.00008: Magnetic microswimmers: Controlling particle approach through magnetic and hydrodynamic interaction Farshad Meshkati, U Kei Cheang, MinJun Kim, Henry Fu We investigate magnetic microswimmers actuated by a rotating magnetic field that may be useful for drug delivery, micro-surgery, or diagnostics in human body. For modular swimmers, assembly and disassembly requires understanding the interactions between the swimmer and other modules in the fluid. Here, we discuss possible mechanisms for a frequency-dependent attraction/repulsion between a three-bead, achiral swimmer and other magnetic particles, which represent modular assembly elements. We first investigate the hydrodynamic interaction between a swimmer and nearby particle by studying the Lagrangian trajectories in the vicinity of the swimmer. Then we show that the magnetic forces can be attractive or repulsive depending on the spatial arrangement of the swimmer and particle, with a magnitude that decreases with increasing frequency. Combining magnetic and hydrodynamic effects allows us to understand the overall behavior of magnetic particles near the swimmer. Interestingly, we find that the frequency of rotation can be used to control when the particle can closely approach the swimmer, with potential application to assembly. [Preview Abstract] |
Monday, November 23, 2015 5:49PM - 6:02PM |
L25.00009: Low Re swimming in suspensions J. Amadeus Puente-Velazquez, Francisco Godinez, Roberto Zenit The swimming performance of force-free magnetic swimmers is studied experimentally for the creeping flow regime. Instead of purely viscous fluids, we consider suspensions of neutrally buoyant particles. Swimmers with both rigid and flexible helical tails are used. We found that in all cases, the swimming speed is enhanced by the presence of particles. As the particle concentration increases, the swimming speed is larger, for a given frequency. The effect is more significant for the case of swimmers with flexible tail. The results are discussed and contrasted with some recent modeling effort. [Preview Abstract] |
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